Compression and cold weld sealing method for an electrical via connection

ABSTRACT

Compression cold welding methods, joint structures, and hermetically sealed containment devices are provided. The method includes providing a first substrate having at least one first joint structure which comprises a first joining surface, which surface comprises a first metal; providing a second substrate having at least one second joint structure which comprises a second joining surface, which surface comprises a second metal; and compressing together the at least one first joint structure and the at least one second joint structure to locally deform and shear the joining surfaces at one or more interfaces in an amount effective to form a metal-to-metal bond between the first metal and second metal of the joining surfaces. Overlaps at the joining surfaces are effective to displace surface contaminants and facilitate intimate contact between the joining surfaces without heat input. Hermetically sealed devices can contain drug formulations, biosensors, or MEMS devices.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.11/267,541, filed Nov. 4, 2005, now U.S. Pat. No. 8,191,756, whichclaims the benefit of U.S. Provisional Application No. 60/625,053, filedNov. 4, 2004. These applications are incorporated herein by reference intheir entirety.

BACKGROUND OF THE INVENTION

This invention is generally in the field of methods and devices forsealing parts together, and more particularly hermetic sealing methodsfor devices and/or implantable medical devices.

In many applications, there is a need to join, bond, or otherwise sealtwo or more parts together. Oftentimes, particularly with medicalimplant devices, these seals must be biocompatible and hermetic, forexample, to protect the purity or quality of the reservoir contents.

Examples of devices that may require sealing are described in U.S. Pat.Nos. 5,797,898, 6,527,762, 6,491,666, and 6,551,838, which areincorporated by reference herein. These devices for the controlledrelease or exposure of reservoir contents include a plurality ofreservoirs in which the reservoir contents are contained. The reservoirsmay contain pharmaceutical formulations for release, sensors forexposure, or combinations thereof. In constructing these devices, itoften is necessary to seal two or more substrates or other parts, whichmay contain the reservoirs and reservoir contents or electroniccomponents associated with operation of the device.

Various sealing approaches are known in the art. Examples include thosedescribed in U.S. Pat. No. 6,730,072 (describing the use of a polymericgasket and backplate) and U.S. Pat. No. 6,827,250 (describing varioustechniques for hermetically sealing micro-reservoirs, including hightemperature laser or resistive welding, soldering, ultrasonic welding,and metal compression gaskets), and in U.S. Patent ApplicationPublication No. 2005/0050859 A1, which are incorporated by referenceherein. These methods may not be suitable or ideal for all sealingapplications.

Under ambient conditions, metal surfaces will not typically bond whenbrought together because the metal surfaces are covered with a surfaceoxide, an organic contaminant, or both, which act as barriers to metalbond formation. However, the compression of two flat metal surfaces atpressures beyond the yield stress of the metals can cause the surfacesto deform, displacing the barriers and exposing clean metal which canbond. Yet, even with significant metal deformation of two flat surfacescompressed together, the actual bonding area is significantly lower thanthe mating surfaces area. (Mohamed & Washburn, Welding ResearchSupplement, September 1975, pp. 302s-310s; Welding & Joining Processes3.371J/13.391J Fabrication Technology, T. Eagar, MIT) This low bondingarea characteristic is due to two phenomena. First, the surface fractionof newly exposed metal is not a strong function of the amount ofdeformation for flat surfaces. Second, asperities prevent the majorityof the surface from interacting and bonding. Because the surfaces arenot completely bonded, leak paths may be present, preventing a hermeticseal from forming.

Ferguson, et. al., “Contact Adhesion of Thin Gold Films on ElastomericSupports: Cold Welding Under Ambient Conditions,” Science, New Series,253(5021): 776-78 (Aug. 16, 1991) discloses a gold-to-gold bond underambient conditions by contacting thin gold metal surfaces on top ofcompliant polymers. However, the result is a bonded interface with“islands” of contaminants that are not bonded. These islands could forma contiguous leak path.

It would be desirable to provide improved sealing methods, for forminghermetic seals at low temperatures with a range of materials. It alsowould be desirable to individually, hermetically seal a plurality ofclosely spaced reservoirs between at least two substrates, in a processthat is relatively simple and cost effective, particularly for largescale production with high reliability.

SUMMARY OF THE INVENTION

In one aspect, compression cold welding methods and structures areprovided for hermetically sealing at least two substrates together. Thisadvantageously can provide a hermetic seal without heat input to thesealing process, which may be desirable in many applications where suchadditional heat could be detrimental to devices, formulations, ormaterials in close proximity to the bonding area.

In a preferred embodiment, the method includes providing a firstsubstrate having at least one first joint structure which comprises afirst joining surface, which surface comprises a first metal; providinga second substrate having at least one second joint structure whichcomprises a second joining surface, which surface comprises a secondmetal; and compressing together the at least one first joint structureand the at least one second joint structure to locally deform and shearthe joining surfaces at one or more interfaces in an amount effective toform a metal-to-metal bond between the first metal and second metal ofthe joining surfaces. In one embodiment, the method further includesaligning the at least one first joint structure above the at least onesecond joint structure before the compressing step so as to impart oneor more overlaps of the at least one first joint structure over the atleast on second joint structure, wherein the one or more overlaps createthe one or more interfaces of the joining surfaces during thecompressing step. In preferred embodiments, the one or more overlaps areeffective to displace surface contaminants and facilitate intimatecontact between the joining surfaces without heat input. In a particularembodiment, the at least one first joint structure comprises at leastone tongue structure and the at least one second joint structurecomprises at least one groove structure, and the step of compressingtogether the at least one first joint structure and the at least onesecond joint structure includes compressing the at least one tonguestructure at least partially into the at least one groove structure. Inone embodiment, the at least one tongue structure has a tongue heightranging from 1 micron to 100 microns and a tongue width ranging from 1micron to 100 microns, and the at least one groove structure has agroove depth ranging from 1 micron to 100 microns and a groove widthranging from 1 micron to 100 microns.

Various combinations of materials of construction may be used. Forexample, the first metal, the second metal, or both, may comprise goldor platinum. In other embodiments, the first metal, the second metal, orboth, comprise a metal selected from the group consisting of gold,indium, aluminum, copper, lead, zinc, nickel, silver, palladium,cadmium, titanium, tungsten, tin, and combinations thereof. The firstmetal and the second metal may be different metals. The first substrate,the second substrate, or both, may comprise silicon, glasses, ceramics,polymers, metals, and combinations thereof. The first joint structure,the second joint structure, or both, may comprise a material selectedfrom the group consisting of metals, ceramics, glasses, silicon, andcombinations thereof. In one embodiment, the first joint structure, thesecond joint structure, or both, may comprise indium, aluminum, gold,chromium, platinum, copper, nickel, tin, alloys thereof, andcombinations thereof.

In one embodiment, the at least one first joint structure is formed bybonding at least one pre-formed structure to the first substrate. Thefirst joining surface may be formed, for example, by an electroplatingprocess, evaporation, a chemical vapor deposition process, sputtering,electron beam evaporation, or a wet etch process. In one embodiment, thefirst joint structure and first joining surface are a layer of metalcovering at least part of a surface of the first substrate.

In one embodiment, the method may further include providing one or morepre-forms between the first substrate and the second substrate, whereinthe step of compressing together the at least one first joint structureand the at least one second joint structure further comprises deformingand shearing the one or more pre-forms at pre-form interfaces with thesubstrates or the joining surfaces. In one embodiment, the pre-formscomprise a metal, a polymer, or a metallized polymer.

In one embodiment, the method further includes heating the joiningsurfaces at the one or more interfaces. The compressing step and theheating step may occur substantially simultaneously. In one embodiment,the heating of the joining surfaces occurs with a microheater.

In another embodiment, the sealing method further includes applying anultrasonic energy to the joining surfaces at the one or more interfaces.

In yet other embodiments, the sealing method further includes clampingor soldering together the first substrate and the second substrate.

In a preferred embodiment of the method, the bonded substrates compriseat least one cavity defined therein. In one embodiment, the at leastfirst substrate comprises a plurality of discrete reservoirs containingreservoir contents, each reservoir being hermetically sealed from eachother and from an exterior environment. In one example, the reservoircontents comprise a biosensor or other secondary device. In anotherexample, the reservoir contents comprise a drug formulation. In stillanother example, the reservoir contents comprise fragrance or scentcompounds, dyes or other colorants, sweeteners, or flavoring agents. Inone embodiment, the first substrate comprises a cavity in which a thirdsubstrate is located before the first and second joint structures arecompressed together. The third substrate may, for example, comprises asensor, a MEMS device, or combination thereof.

In one embodiment, the deformation step in the process is conductedunder vacuum or in an inert gas atmosphere effective to reduce oxidationof the joint structure relative to that which would occur if conductedin atmospheric air.

In one embodiment, a method is provided for hermetically sealing atleast two substrates together, which includes the steps of providing afirst substrate having at least one first joint structure whichcomprises a first joining surface, which surface comprises a firstcompliant polymer, which has been metallized with a thin layer of ametal; providing a second substrate having at least one second jointstructure which comprises a second joining surface, which surfacecomprises a second compliant polymer, which has been metallized with athin layer of a metal; and compressing together the at least one firstjoint structure and the at least one second joint structure to locallydeform the joining surfaces at one or more interfaces in an amounteffective to form a bond between the first and second the joiningsurfaces. In one embodiment, the layer of metal of the first or secondmetallized polymer, or both, comprises gold, platinum or a combinationthereof.

In another aspect, a containment device is provided which includes afirst substrate having a front side and a back side, and including atleast one first joint structure which comprises a first joining surface,which surface is a first metal; a second substrate having at least onesecond joint structure which comprises a second joining surface, whichsurface is a second metal; a hermetic seal formed between and joiningthe first substrate and the second substrate, wherein the hermetic sealis made by compression cold welding the first joining surface to thesecond joining surface at one or more interfaces; and at least onecontainment space being defined between the first substrate and thesecond substrate within the hermetic seal such that the containmentspace is hermetically sealed an exterior environment. In one embodiment,the at least one containment space comprises a plurality of discretereservoirs in the at least first substrate positioned between the frontside and the back side. In various embodiments, the at least onecontainment space comprises a sensor, a MEMS device, a drug formulation,or a combination thereof, contained in said containment space. In apreferred embodiment, the joining surfaces are joined together by ametal-to-metal bond formed without heat input. In one embodiment, the atleast one first joint structure and the at least one second jointstructure comprise a tongue and groove joint.

In various embodiments, the first metal, the second metal, or both,metals may comprise gold, platinum, or a combination thereof, and thesubstrates may comprise a material selected from the group consisting ofsilicon, metals, ceramics, polymers, glasses, and combinations thereof.In one embodiment, a pre-form structure is deformed between the firstand second joint structures. In another embodiment, the first jointstructure or the second joint structure comprises a microheater.Optionally, an intermediate layer may be provided adjacent to themicroheater. In one embodiment, the first joint structure or secondjoint structure may comprise a magnetic material effective to heat thestructure via an external induction heater.

The device may further include other securement means, for example, aclamp may be included for joining the substrates together, or a soldermaterial may be used to secure the first substrate and the secondsubstrate together.

In one embodiment, the first substrate further comprises a plurality ofdiscrete openings in communication with the at least one containmentspace, and said openings are closed by a plurality of discrete reservoircaps. In one embodiment, the reservoir caps comprise a metal film andthe device includes means (e.g., control circuitry and power source) forselectively disintegrating the reservoir caps.

In one aspect, an implantable medical device is provided for thecontrolled exposure or release of contents located in hermeticallysealed reservoirs. In one embodiment, the device includes a firstsubstrate; a plurality of discrete reservoirs disposed in the firstsubstrate, the reservoirs having first openings and second openingsdistal the first openings; reservoir contents located inside thereservoirs, wherein the reservoir contents comprises a drug or abiosensor; a plurality of discrete reservoir caps closing the firstopenings; means for selectively disintegrating the reservoir caps; and asecond substrate and a hermetic joint sealing and closing the secondopenings, wherein the hermetic joint is made by compressioncold-welding. In one embodiment, the hermetic joint comprises a tongueand groove interface.

In another aspect, a method is provided for forming an electrical viaconnection comprising: providing a first non-conductive substrate havingan aperture therethrough, wherein the interior surface of said firstsubstrate defining said aperture comprises a layer of a firstelectrically conductive material; providing a second non-conductivesubstrate having a projecting member extending from a surface of saidsecond substrate, wherein said member is formed of or coated with asecond electrically conductive material; and compressing the projectingmember of said second substrate into the aperture of said firstsubstrate, to locally deform and shear the first and/or secondelectrically conductive layers, in an amount effective to form a bondand electrical connection between the first and second electricallyconductive layers.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a cross-sectional view of one embodiment of a seal systemhaving a tongue and groove joint structure design which provides ahermetic seal formed by a compression cold weld process.

FIG. 2 is a cross-sectional view of another embodiment of a hermeticseal system having a tongue and groove joint structure design, whichprovides a hermetic seal. The figure on the left shows the structurebefore the compression cold weld process, and the figure on the rightshows the seal formed after the compression cold weld process.

FIG. 3 is a scanning electron micrograph showing a cross-section of ahermetic seal that was made using the seal design and compression coldweld process illustrated in FIG. 2.

FIG. 4 is a cross-sectional view of one embodiment of a hermetic sealsystem having a joint structure design having a single cold weldingshear layer at each joint structure.

FIG. 5 is a cross-sectional view of one embodiment of a hermetic sealsystem having metal pre-forms which can be compression cold weldedbetween joint structures.

FIG. 6 is a cross-sectional view of another embodiment of a hermeticseal system having metal pre-forms which can be compression cold weldedbetween joint structures.

FIG. 7 is plan views of five different embodiments of joint structurebase shape geometries.

FIG. 8 is plan views and cross-sectional views of six differentembodiments of joint structure designs that can be used in compressioncold welding to form a hermetic seal.

FIG. 9 is cross-sectional views of four embodiments of hermetic sealsystems formed with different combinations of the joint structuredesigns illustrated in FIG. 8.

FIG. 10 is a cross-sectional view and a magnified cross-sectional viewof an embodiment of a hermetic seal system having a tongue and groovejoint structure design.

FIG. 11 is a cross-sectional view of one embodiment of a hermetic sealsystem having heaters and intermediate layers on the heaters.

FIG. 12 is a cross-sectional view of one embodiment of a hermetic sealsystem having microheaters on a joint structure core comprising asubstrate material and intermediate layers on the microheaters.

FIG. 13 is a cross-sectional view of one embodiment of a hermetic sealsystem having microheaters in direct contact with a joining surfacematerial.

FIG. 14 is a cross-sectional view of one embodiment of a hermetic sealsystem having microheaters on a joint structure core comprising asubstrate material and in direct contact with a joining surfacematerial.

FIG. 15 is a perspective view of one embodiment of a hermetic sealsystem having a Nitinol clamp.

FIGS. 16A-C are cross-sectional views of one embodiment of a hermeticseal system having a solder clamp, showing the assembly steps.

FIG. 17 is a cross-sectional view of one embodiment of a hermetic sealsystem having a cold weld clamp and a compression seal material.

FIG. 18 is a cross-sectional view of one embodiment of a device thatincludes an array of reservoirs that have each been individuallyhermetically sealed use a compression cold welding process with a tongueand groove joint design. The body of the device in which the reservoirsare defined comprises two substrate portions that also have beenhermetically sealed together using a compression cold welding processwith a tongue and groove joint design.

FIG. 19 is a perspective view of one embodiment of a device thatincludes an array of reservoirs and having a joint design forindividually hermetically sealing the reservoirs using a compressioncold welding process.

FIG. 20 is cross-sectional views of three embodiments of hermetic sealsystems having various polymer joint structures plated with metaljoining surfaces.

FIG. 21 is a cross-sectional view of an embodiment of a multi-reservoircontainment device, illustrating the hermetic sealing of the reservoirsby a compression cold welding process.

FIG. 22 is a cross-sectional view of one embodiment of a sealedstructure using a bonded “sandwich” structure to protect an intermediatesubstrate which is not subjected to compressive bonding forces.

FIG. 23 is cross-sectional view of one embodiment of parts, prior tobonding, for forming an electrical via connection by compression coldwelding as described herein.

FIGS. 24A-B are perspective views of an electrical wire connection madeby compression cold welding as described herein. FIG. 24A shows theparts before connection, and FIG. 24B shows the connected assembly.

FIG. 25 is a perspective, cross-sectional view of one embodiment ofparts, prior to bonding, for forming an electrical via connection bycompression cold welding.

FIG. 26 is a perspective view of one embodiment of an electrical viaconnection made by compression cold welding. The illustration shows thematerial overlap between the aperture and tooth.

FIGS. 27A-B are scanning electron micrographs (SEMs) of two siliconsubstrates having microfabricated seal features for compression coldwelding.

DETAILED DESCRIPTION OF THE INVENTION

Methods and devices have been developed to form a hermetic seal by acompression cold welding process. The process and seal designsadvantageously permit device parts to be bonded together reliably andefficiently, while protecting sensitive device components and contentsfrom heat and solvents. The sealing process involves compression andcold welding together two substrates that are provided with one or morejoint sealing surfaces that, during a compression step, locally deformand shear to promote intermolecular diffusion and bonding.Advantageously, the shearing and deformation of metal sealing surfacessubstantially scrub away any metal oxides or organic or inorganiccontaminants present on the surface, thereby providing an atomicallyclean metal surface to promote metal-to-metal bonding between thejoining surfaces and thus hermeticity. That is, cold welding createsjoining surfaces that are free of contaminants and thus free to bond. Ina preferred cold welding process, pressures above the yield stress ofthe metal cause the joining structures and joining surfaces to deform.The metal deformation serves two purposes: It creates intimate contactbetween the joining surfaces, and it displaces surface oxides and othercontaminants so that metal-to-metal bonding can occur. In embodimentswhere a metal-to-metal bond is formed by cold welding, additional clampsmay be unnecessary.

In one aspect, a method is provided for hermetically sealing at leasttwo substrates together, which includes the steps of providing a firstsubstrate having at least one first joint structure which comprises afirst joining surface, which surface comprises a first metal; providinga second substrate having at least one second joint structure whichcomprises a second joining surface, which surface comprises a secondmetal; compressing together the at least one first joint structure andthe at least one second joint structure to locally deform and shear thejoining surfaces at one or more interfaces in an amount effective toform a metal-to-metal bond between the first metal and second metal ofthe joining surfaces. The first metal and second metal may be the sameor different. They could be different alloys of the same base metal. Ifthe same metal, the first metal and the second metal may have differentstructural morphologies, e.g., crystal structures, grain structure, etc.Non-limiting examples of suitable metal surface materials includeindium, aluminum, copper, lead, zinc, nickel, silver, palladium,cadmium, titanium, tungsten, tin, and combinations thereof. Gold orplatinum may be preferred. The first substrate, the second substrate, orboth, may be formed of various materials, such as silicon, glasses,ceramics, polymers, metals, and combinations thereof. Non-limitingexamples of substrate materials include quartz, borosilicate glass,aluminum oxide in any of its forms, silicon nitride, and combinationsthereof. The substrate and the at least one joint structure may becomprised of the same material or different materials. The jointstructure may be formed in/on the substrate by a variety of processesknown in the art. Examples include deep reactive ion etching, drilling(e.g., laser), milling, micro-machining, MEMs processing, or LIGAprocessing of the substrate. The first joint structure, the second jointstructure, or both, may comprise a material selected from metals,ceramics, glasses, silicon, and combinations thereof. Examples ofpossible joint structure materials include the metal surface metalsmentioned above, such as indium, aluminum, gold, chromium, platinum,copper, nickel, tin, alloys thereof, and combinations thereof, as wellas alumina in any of its forms, quartz, fused silica, silicon oxide,aluminum nitride, silicon carbide, and diamond. The joint structures maybe integral with the substrate or bonded to it. In one embodiment, thejoint structure is formed by bonding at least one pre-formed structureto its substrate. This pre-formed structure could be formed, forexample, by electroplating, chemical vapor deposition, sputtering, MEMSprocessing, micro-machining, LIGA processing, or anodic bonding. Thepre-form structure can be attached to the substrate, for example, bythermocompression, soldering, or ultrasonic welding. The joint structureand its joining surface may be comprised of the same material ordifferent materials.

In one embodiment, the method further includes providing one or moreseparate pre-forms between the first substrate and the second substrate,wherein the step of compressing together the at least one first jointstructure and the at least one second joint structure further comprisesdeforming and shearing the one or more pre-forms at pre-form interfaceswith the substrates or the joining surfaces. The pre-form may be formed,for example, by LIGA processing, MEMS processing, wet etching, lasermicro-machining, stamping, cutting, or micro-casting. The pre-forms maycomprise a metal, a polymer, or a metallized polymer.

In preferred applications of these methods and seal designs, thehermetic seals are used in sealing microfabricated device components,particularly implantable medical devices. In a preferred embodiment, thepresent sealing methods and joint structures are used in a device toindividually seal an array of containment reservoirs loaded withreservoirs contents, such as drugs for controlled release and/orbiosensors, and/or to package associated electronic components foroperating the device.

In one aspect, a device is provided that incorporates one or more ofthese hermetic seals. In one embodiment, the device includes a firstsubstrate (which may include two or more wafers or substrate portions)having a plurality of reservoirs each of which contain a sensor or drugformulation, where each reservoir includes a first opening at a firstsurface of the device. The first opening is closed by a reservoir capthat can be selectively and actively disintegrated to control the timeand/or rate of release or exposure of the reservoir content. In oneembodiment the reservoir further includes a second opening distal to thefirst opening. This opening is hermetically sealed after orsimultaneously with loading of the reservoir contents into thereservoir. Typically, this sealing involves bonding the first substrateto a second substrate, using one or more of the hermetic sealing methodsand joint designs described herein. Optionally, the device furtherincludes a packaging structure hermetically bonded to a surface of thefirst or second substrate, to protect electronic components associatedwith powering and controlling the reservoir cap disintegration and anyreservoir based sensors. The packaging structure and hermetic sealsprotect the electronic components and reservoir contents from theenvironment. As used herein, the term “environment” refers to theenvironment external the reservoirs, including biological fluids andtissues at a site of implantation, air, fluids, and particulates presentduring storage or during in vitro or in vivo use of the device.

As used herein, the term “cold weld” means an intermolecular bond formedwithout the application of heat, with ambient conditions typically lessthan 40° C.

As used herein, the term “hermetic seal” refers to preventingundesirable ingress or egress of chemicals into or from one or morecompartments of the device, particularly the device reservoirs, over theuseful life of the device. For purposes herein, a seal that transmitshelium (He) at a rate less than 1×10⁹ atm*cc/sec is termed hermetic.

As used herein, the terms “comprise,” “comprising,” “include,” and“including” are intended to be open, non-limiting terms, unless thecontrary is expressly indicated.

Device Components and Materials

The hermetic seal comprises a first substrate having at least one firstjoint structure with a first joining surface and a second substratehaving at least one second joint structure with a second joiningsurface, bonded at one or more interfaces by cold welding. In preferredembodiments, the seals are biocompatible and suited for medicalimplants. In one embodiment, the two substrates may optionally containone or more of reservoirs, sensors, drugs, and electronics. Thesubstrates may comprise, silicon, glass, Pyrex glass, stainless steel,titanium, alumina, silicon nitride, and other biocompatible ceramics andother metals or polymers. In one embodiment, silicon substrates allowfor use of optical probes in the near-infared (NIR) to infrared (IR)spectrum. It is understood that spectroscopic methods using light in thevisible, UV or other wavelengths may be possible by an appropriateselection of substrate material. In addition, the substrate may comprisepolymers with high enough Young's Modulus and yield stress to cause highshear during cold welding.

The joint structures (also called “sealing features”) on each substratemay comprise the same or a different material than the substrate. Forinstance, if the joint structures are micro-machined into the substrate,the joint structures are comprised of the substrate material.Alternatively, the joint structures may be a pre-form bonded to thesubstrate comprised of a different material than the substrate, such asa metal, a metal alloy or a combination of metals. In anotherembodiment, a LIGA formed nickel joint structure could be electroplatedwith a layer of gold and then bonded to a metallized substrate using asolder, braze, or thermocompression bond. The LIGA structure could becomprised of any metal or metal alloy compatible with the LIGA process.In yet another embodiment, the joint structure pre-form could be formedfrom glass or silicon using microelectromechanical system (MEMS)fabrication.

The joint structures have joining surfaces (also called “shear layers”or “bonding surfaces”) which are preferably metal and optionally maybond to other joining surfaces. In an alternate embodiment, described infurther detail below, the joining surface may be a compliant polymer.Metals with a suitably low plastic deformation stress are used as ajoining surface. Suitability can be determined by one skilled in theart, for example, based on the particular joint geometry and the amountof force that can reasonably be applied to form the joint. In addition,metals that do not have a surface oxide or have a high relative oxide toparent metal hardness are preferable for use as a joining surface. SeeTylecote, “Investigations on Pressure Welding” British Welding J. (March1954) and Mohamed, et al., “Mechanism of Solid State Pressure Welding”Welding Research Supplement, pp. 302-10 (September 1975). Representativeexamples of suitable metals (and their alloys) include gold (Au), indium(In), aluminum (Al), copper (Cu), lead (Pb), zinc (Zn), nickel (Ni),silver (Ag), platinum (Pt), palladium (Pd), and cadmium (Cd).Representative examples of joining surface metals preferred forbiocompatibility include gold and platinum.

The first joining surface may or may not be comprised of the samematerial as the second joining surface with which the first joiningsurface will form the hermetic seal. For example, the joining surfacesmay be comprised of dissimilar metals or different alloys of the sameparent metal. For example, the first joining surface may be gold whilethe second is platinum. In one embodiment, the joining surfaces arecomprised of the same material with a different structural morphology.For instance, a first joining surface may be annealed to reduce theyield stress through the normal annealing mechanisms of recovery,recrystallization, and grain growth, while the second joining surfacemay be deposited in such a way that the grain size is small, thusincreasing the yield stress.

The joining surfaces may comprise the same or a different material thanthe joint structures. This allows greater freedom in the fabricationmethod of the joint as well as more design control over the extent andlocation of plastic deformation. For instance, accurate joint structurescan be micromachined on a silicon substrate and the joint surfacematerial can be deposited on those structures using established MEMsprocess steps. However, forming accurate joint structures in an aluminasubstrate may prove difficult and may require alternative materials andfabrication methods. As an example, for alumina substrates, the jointstructure may be a deposited metal or alloy with different mechanicalproperties (e.g., higher elasticity and higher yield stress) than thejoining surface. In one embodiment, the joint structure could be anelectroplated nickel, an electroplated gold alloy, an electroplatedchromium structure, or an electroplated platinum structure. Therefore,it should be understood that a joint structure may need no furtherprocessing and have a joining surface comprising the same material asthe joint structure, or the joint structure may have at least one othermaterial deposited, electroplated, or formed on the joint structuresurface to create a joining surface comprising a different material thanthe joint structure material. The joint structure may be comprised of asingle material or a combination of materials.

Methods of Making a Hermetic Seal

The hermetic seals are made by compression and cold welding. In oneembodiment, two substrates are hermetically sealed together by providinga first substrate having at least one first joint structure whichcomprises a first joining surface which is a metal, providing a secondsubstrate having at least one second joint structure which comprises asecond joining surface which is a metal, compressing together at leastone first joint structure and at least one second joint structure tolocally deform and shear the metal surfaces at one or more interfaces inan amount effective to form a continuous metal-to-metal bond between thejoining surfaces at the one or more interfaces.

In some embodiments, ultrasonic energy may be introduced to the hermeticseal joint during the bonding process. While not being bound to anyparticular mechanism of action, it is believed that the ultrasonicenergy may improve the hermetic seal by causing metal-to-metalinter-diffusion by scrubbing the contaminants out of the joiningsurfaces and deforming the surface asperities so there is intimatecontact at the bonding interface.

In other embodiments where the bonding mechanism is not purely coldwelding, a pulse of heat or a small increase in temperature may aid inmetal bonding by increasing diffusion and lowering the metal's yieldstress. For example, induction heating could be used to locally heat thejoining surface metals. If other metals are present in the device andare non-magnetic, the joining metals can be selectively heated byincorporating a magnetic material under the joining surfaces.Representative examples of magnetic materials include nickel, iron,cobalt, and combinations thereof. Alternatively, the joint structuregeometry may be designed to selectively couple a magnetic field of agiven frequency. (See Cao et al., “Selective and localized bonding usinginduction heating”, Solid-State Sensor, Actuator and MicrosystemsWorkshop, Hilton Head Island, S.C., Jun. 2-6, 2002.)

Generally, the ambient environment may be displaced with forming gas,nitrogen, vacuum, or some other condition which would minimize the rateof oxidation and contamination of the joining surfaces as the hermeticbond is formed.

Illustrative Embodiments of the Hermetic Sealing Devices and Systems

Joint structures have been designed to efficiently create large localpressures and deformations at the joining surfaces for a given load.FIGS. 1-6 illustrate cross-sectional views of embodiments of hermeticseal systems having joint structures that efficiently convert acompressive force on the substrates into a shear force on the joiningsurfaces to cold weld the joint structures together. The shear force isproduced by an interference or overlap between the joint structures suchthat when the joint structures are brought together, there is anoverlapping portion of the metal joining surfaces that is deformed bycompressive forces. The relative shear of the two overlapping structureseliminates asperities and allows the surfaces to interact and bond. Insome embodiments, only the interfering portion of each joint structurewill be substantially deformed. In other embodiments, only one jointstructure of a pair of joint structures forming a hermetic seal issubstantially deformed due to the different materials and associatedproperties used to form each half of the joint.

The joint structures illustrated in FIGS. 1-6 can be fabricated usingconventional MEMs processes, for example, although the structures shouldalso function similarly on a macro-scale. FIGS. 1-6 illustrate only oneset of joint structures on each hermetic sealing system, but otherembodiments may include multiple sets of joint structures. In addition,the joint structures in FIGS. 1-6 are represented with a rectangularcross-section, but other cross-sections, such as a triangular,rhombus-shaped, or hemispherical joint structure, may also be employed,depending, for example, on the micro-machining limits of geometrydefinition. For example, a hemispherical joint structure can be createdby electroplating a joint structure material onto aphoto-lithographically defined seed layer in the absence of a platingmold. In another embodiment, reactive ion etching (RIE) can be used toform a rounded or circular joint structure from a rectangular siliconstructure. In yet another embodiment, photoresist can be overexposed andthus undercut during development to form a rhombus-shape which can thenbe used as a mold for electroplating a joint structure. Multiple layersof photoresist may be used to create more complicated featuregeometries.

FIG. 1 illustrates a cross-sectional view of one embodiment of ahermetic seal system 10 having a “tongue and groove” joint structuredesign which can be sealed by cold welding. The hermetic seal system 10has a first substrate 12 which has first joint structures 16. The firstjoint structures each have a first joining surface 18. A secondsubstrate 14 has second joint structures comprising two joint structureelements 20 a and 20 b. Each second joint structure 20 a/20 b has asecond joining surface 22. The first joint structures 16 create a“tongue” which fits at least partially into a “groove” created by thesecond joint structures 20 a/20 b. The width of the tongue as measuredacross opposite sides of sealing surfaces 18 is greater than the spaceprovided in the groove of the second joint structures joining layer 22.Thus, the first joint structures joining layer 18 and/or the secondjoint structures joining surface 22 are deformed as the joiningstructures are compressed together during cold welding, creating shearalong the top corners and sidewalls of each joint structure at thejoining surfaces 18 and 22.

The first joining surface 18 and the second joining surface 22 may becomprised of the same or different materials. FIG. 1 illustrates onelayer of material forming the joining surfaces 18 and 22 and a differentmaterial forming the respective joining structures 16 and 20 a/20 b. Inanother embodiment, the joining surfaces and/or the joining structuremay include multiple layers of materials to fine tune the mechanical orcold weld bonding properties.

FIG. 2 illustrates a cross-sectional view of another embodiment of ahermetic seal system 30 before and after formation of a hermetic sealusing cold welding. The hermetic seal system 30 has a first substrate 32and a second substrate 34. The first substrate 32 has a first jointstructure 40, having a metal joining surface 38 a/38 b. The first jointstructure 40 is in the form of a groove structure formed into the firstsubstrate 32. The second substrate 34 has a second joint structure 36comprising a different material than the second substrate. The secondjoint structure 36 has a metal joining surface 42 a/42 b comprising thesame material as the second joint structure. This second joint structure36 is in the form of a tongue structure, which may partially fit intothe groove structure of the first joint structure 40.

A compressive bonding force is applied to the first substrate 32 to coldweld the two substrates together. As the compressive force is applied,the tongue of the second joint structure 36 is deformed into the grooveof the first joint structure 40. The deformation arises when the forceapplied to the area of interference between the first joint structure 40and the second joint structure 36 results in a pressure exceeding theyield stress of 36. The interference or overlap also creates shearforces at the interface where the joining surfaces 38 a/38 b, 42 a/42 bmeet. The combination of deformation and shear forces form ametal-to-metal bond between the joining surfaces 38 a and 42 a andjoining surfaces 38 b and 42 b. Thus, an effective hermetic seal isformed by using cold welding. As shown in the cold welded structure onthe right side of FIG. 2, the tip end portion 41 of the tongue structure36 does not extend into the groove structure 40 enough to contact theinner bottom surface 31 of the groove structure. See, e.g., FIG. 3.

It should be understood that the overlap between the joint structures inFIG. 2 is shown for illustrative purposes and may be smaller or largerthan shown. The larger the overlap, the greater the compressive forcerequired to deform the joining layers and thus form a hermetic bond.

In addition, it should be understood that the local deformation at thejoining surfaces is a function of the mechanical properties of both thejoint structure and the joint surface. For example, in one embodiment,an entire joint structure comprising a solid gold tongue may deformunder compression into a silicon groove joint structure. In anotherembodiment, if the tongue joint structure is silicon and the joiningsurface is gold, the deformation is localized to the sides and cornersof the tongue joint surface.

FIG. 4 illustrates a cross-sectional view of an embodiment of a hermeticseal system 50 having one cold welding shear layer at each jointstructure. The hermetic seal system 50 has a first substrate 52 and asecond substrate 54. In this embodiment, the first joint surface 58overlaps with the second joint surface 62 on one side. Having overlap onone side, instead of two sides, of the joint surfaces 58 and 62 mayallow a reduction in the overlap required to form a hermetic seal. Areduction in the overlap reduces the compressive force required to formthe hermetic seal by cold welding because the yield stress is achievedwith a lower force. In an alternate embodiment, the joint structures maybe in the form of a triangular or trapezoidal joint structurecross-section to further reduce the shear force required to form thehermetic seal. One disadvantage of this joint design is that only onesealing perimeter can be created, while with a symmetric design (e.g.,FIG. 2) there is an opportunity to create two sealing perimeters. Asingle joint structure such as the tongue and groove combinationdescribed herein is generally considered to have two perimeters.Multiple sealing perimeters may advantageously provide a desirableredundancy in a device, providing a “fail-safe” hermetic seal, whereinone or more, but less than all, of the sealing perimeters may beincomplete, or may fail, and the overall seal remains hermetic.

Another embodiment of a hermetic seal system 70 using cold welding isillustrated in FIG. 5. The first substrate 72 and a second substrate 74are shown before compressive force is applied. The first substrate 72has first joint structures 76 a/76 b which have a metal joining surface78. The first joint structures 76 a/76 b are aligned with second jointstructures 80 a/80 b, having a metal joining surface 82. Both jointstructures 76 a/76 b and 80 a/80 b form a groove in which a metalpre-form 84 is entrapped. As the first substrate 72 and the secondsubstrate 74 are compressed together during cold welding, the pre-form84 is deformed and sheared against the joining surfaces 78 and 82 toform metal-to-metal bonds between the perform and the joining surfaces.

The pre-form 84 may be formed using a LIGA process, wet etch, or lasermicro-machining. It should be understood that the processing of thepre-form 84 is dependent upon compatibility of the process with thematerial used as the pre-form. It should also be understood that thepre-form's cross-sectional geometry may be limited by the fabricationmethod used. For example, a LIGA technique cannot produce a circularcross-section as illustrated in FIG. 5, but a micro-casting process mayenable such a cross-section.

FIG. 6 illustrates a cross-sectional view of another embodiment of ahermetic seal system 90 having a metal pre-form which may be cold weldedbetween two joint structures. The hermetic seal system 90 has a firstsubstrate 92 and a second substrate 94. The first substrate 92 has firstjoint structures 96 comprising groove structures formed in the firstsubstrate. The first joint structures 96 have a first metal joiningsurface 98. The second substrate 94 has second joint structures 100comprising groove structures formed into the substrate and a secondmetal joining surface 102. Entrapped between the first joint structures96 and the second joint structures 100 is a metal pre-form 104. Thepre-form 104 can be formed using methods similar to the methodsdescribed above in reference to the perform 84 in FIG. 5. As the firstsubstrate 92 and the second substrate 94 are compressed together, thepre-form 104 is deformed and sheared against the joining surfaces 98 and102 to form metal-to-metal bonds between the performs and the joiningsurfaces to complete the hermetic seal.

Various combinations of preforms, positive features (e.g., a “tongue” ora “tooth”) and groove may be used in the compression cold-weldingprocess. In one embodiment, a tongue joint structure on one substrateand a groove joint structure on another substrate having a groove widthlarger than the width of the tongue joint structure may be cold weldedtogether by compressing a pre-form between them.

The pre-form cross-sectional geometry could be circular, an annulus, arectangle or other suitable cross-section.

In all of the above embodiments, it may be desirable to minimize thedistance between the bonded substrates. This adjustment can beaccomplished by minimizing the overlap so that the amount of metaldeformed into the space between the substrates is minimized.Additionally, a groove may be created adjacent to a tongue jointstructure to provide a volume below the substrate surface for thedeformed metal to occupy. Alternatively, the groove structure may havetwo different widths, a wider opening and a narrower distal end so thatmetal sheared by the narrower groove flows into the wider groove at theopening.

FIG. 7 illustrates a top view of various embodiments of joint structurebase geometries which can be used to form hermetic seals using coldwelding. Suitable geometries for the base shape of the joint structureinclude circle 110, oval 112, hemispheres connected with straightsidewalls 114, square with filleted corners 116, and hexagon 118. Otherembodiments of joint structure geometries may include any polygon or anarbitrary path that creates a closed profile. Preferably, sharp cornersalong the joint structure perimeter are avoided because it may bedifficult to form a hermetic seal in such a corner.

FIG. 8 illustrates top views and cross-sectional views of variousembodiments of joint structure designs that can be fabricated using MEMsprocesses. These embodiments have only one joint structure set on eachsubstrate, but other embodiments may include an array of circumscribingteeth or grooves serving as multiple joint structure sets. The “tongue”and “groove” geometries are represented in FIG. 8 with a rectangularcross-section, but other cross-sections, such as a triangular orhemispherical geometries, may also be used, depending on themicro-machining limits of cross-section geometry definition. In otherembodiments, the substrate may contain an array of reservoirs for drugcontent or sensors, where each reservoir is required to be hermeticallysealed from the other reservoirs and the outside environment.

The joint structures 124 a/124 b and 132 of joint structure designs 120and 128 can be fabricated into silicon substrates 122 and 130,respectively, using one and two step deep reactive ion etching (DRIE),respectively, followed by a metal joining surface deposition step. Jointstructures 132 and 124 a/124 b are the MEMs equivalent of a tongue andgroove joint, respectively. During cold welding of substrate 122 tosubstrate 130, the corners of the grooves between joint structures'elements 124 a and 124 b create high localized stress at the edges ofjoint structures 132 (the tooth) and the corners of the groove elements124 a and 124 b. The high stress causes plastic deformation and shear atthe metal interfaces, resulting in intimate contact and bonding betweenthe joining surfaces 126 and 134.

Other embodiments of joint structure designs could be created on a metalsubstrate by using a combination of milling and plunge electrondischarge machining (EDM) steps to create the joint structures and aplating step to metallize the joint structures if necessary.

Joint structure design 136 incorporates tongue joint structures 140 madeof a low plastic deformation stress metal, such as indium, aluminum,gold, or copper. Joint structure design 136 has a transparent substrate138. A Pyrex or similarly transparent substrate, such as sapphire, otherglass chemistries, allows the contents of a hermetically sealed deviceto be optically probed and allows for improved alignment proceduresduring the cold welding process. The formation of the joint structures140 from a different material than the substrate 138 obviates the needfor creating features in the substrate itself. In addition, jointstructure design 136 creates a more deformable joint structure 140 thanjoint structure design 128 by using a metal with a low plasticdeformation stress. Thus, the joint structure 140, with its greaterdeformation capability, may therefore improve the hermetic seal formedby cold welding.

Joint structure design 142 illustrates a soft deformable metal joiningsurface 146 to be cold welded to joint structures similar to the jointstructures 132, 140, 152, and 160 a/160 b of joint structure designs128, 136, 148, and 156, respectively. Joint structure design 142 allowsthe high local stress from a joint structure protruding from a substrateto cause a groove in the metallized joining surface 146 during coldwelding compression. One non-limiting example of a suitable metal foruse as the joining surface 146 is gold. The advantage of joint structuredesign 142 is that alignment issues are greatly reduced. However, jointstructure design 142 may be considerably harder to cold weld since theflat joining surface 146 does not efficiently convert the compressionforce into a shear deformation.

Joint structure design 148 has joint structures 152, which are hybridjoint structures comprised of more than one material, both of which arenot the substrate 150 material. Since the joint structures 152 are notformed from the substrate 150 material, modification of deformationcharacteristics of joint structures 152 can be accomplished withoutmicro-machining the substrate 150. In addition, the joint structures 152can be comprised of nickel its alloys, or other high Young's Modulus andyield stress material to increase the joint structure's stiffness. Thejoint structures 152 are subsequently sputter coated with a seed layerfor plating joining surfaces 154, which can be indium or gold, forexample.

Alternatively, the joint structures 152 could be comprised of adifferent alloy of the joining surfaces 154 material. In one embodiment,an electroplating deposition process used to deposit the jointstructures 152 onto the substrate 150 can also be used to deposit adifferent alloy as the joining surfaces 154 by changing the plating bathcomposition during the electroplating process. For example, a hard goldalloy could be plated initially as the joint structures 152, followed bya softer pure gold as the joining surfaces 154.

Joint structure design 156 allows for creation of groove jointstructures in conditions where it is not convenient to micro-machine arecessed feature into a substrate 158. A groove is defined by twoconcentric protruding joint structure elements 160 a/160 b and can befabricated using a process similar to the process described above inreference to joint structure design 148 and joint structures 152.

FIG. 9 illustrates cross-sectional views of various embodiments of thehermetic seal systems comprising various combinations of the jointstructure designs illustrated in FIG. 8. Hermetic seal system 170comprises joint structure design 120 in combination with joint structuredesign 128. Hermetic seal system 172 comprises joint structure design120 in combination with joint structure design 136. Hermetic seal system174 comprises joint structure design 142 in combination with jointstructure design 128. Hermetic seal system 176 comprises joint structuredesign 142 in combination with joint structure design 136.

Dimensions

FIG. 10 illustrates a cross-sectional view and a magnifiedcross-sectional view of an embodiment of a hermetic seal system 180having tongue and groove joint structure design. The joint structures182 a/182 b and 184 are formed in the silicon substrates by deepreactive ion etching (DRIE). The geometric dimensions of the jointstructures 182 a/182 b, 184 include a groove depth 186, groove width187, a tongue width 188, and a tongue height 190. Preferably, thesegeometric dimensions are in the range of about 1 micron to about 100microns. The tongue and groove joint structures 184 and 182 a/182 b,respectively, are fabricated to create an overlap (also called an“interference”) that exceeds the tolerance in the fabrication of thejoint structures and the accuracy tolerance of the assembly equipment toinsure that the joint surfaces overlap at all points along the hermeticsealing perimeter. In preferred embodiments, the overlap is in the rangeof about 1 micron to about 20 microns and is smaller than one quarter ofthe tongue width 188.

In embodiments wherein the joining surface comprises a differentmaterial than the joint structure material and metallization is used tocreate the joining surfaces, the thicknesses of the metallized joiningsurfaces are between about 0.1 μm and about 50 μm. Metal thicknesses ofabout 1 μm can be created by, vapor deposition, for example. Greatermetal thicknesses can be created by electroplating processes, forexample.

Thermocompression Bonding with Pulsed Heating

In some embodiments of the present invention, selective pulsed heatingmay be used in thermocompression bonding to form a hermetic seal. Theselective pulsed heating may be provided by micro-resistive heaters.Examples of micro-resistive heaters are described in U.S. Pat. No.6,436,853 to Lin et al. Heaters may be incorporated into any of theembodiments of hermetic sealing systems described herein. Suitableheaters can be placed into one of two groups, heaters with anintermediate layer and heaters without an intermediate layer.

Heaters may require an intermediate layer between the heater and anothersurface for any combination of the following three reasons: (1)Depending on the electrical resistivity of the materials being used andthe amount of heating required, the heater material may need to beelectrically insulated from the joining surface and/or the substrate.(2) An intermediate layer may be required in embodiments where thedifferences in the coefficient of thermal expansion (CTE) between theheater and adjacent materials is large enough to potentially introduceunacceptable stresses at the hermetic seal. During heating, thesestresses may manifest themselves by causing delamination, fracturing, orcracking at various interfaces if the stresses exceed the bond strengthbetween the heater and adjacent materials or if the stresses exceed theultimate tensile strength of any of the materials at the hermetic seal.(3) An intermediate layer may be required as a diffusion barrier toprevent the electrical characteristics of the heater from changing withrepeated heating cycles or to slow the diffusion of adhesion layers.Thus, intermediate layers may be required for electrical isolation, forCTE mismatch, for a diffusion barrier, or for any combination of thethree depending on the specific materials used.

For simplicity, the intermediate layer between the heater and substrateor any adhesion layers at material interfaces have not been shown in theFIGS. 11-14. Only the intermediate layer between the heater and thejoining surface has been shown.

FIG. 11 illustrates a cross-sectional view of one embodiment of ahermetic seal system 200 having heaters 218. The heaters 218 aredisposed on a second substrate 212. Intermediate layers 220 are disposedon top of the heaters 218. A joining surface material 222 is heated frombelow the intermediate layers 220 by the heaters 218. A hermetic seal isformed when the first substrate 210 is joined together with the secondsubstrate 212 and material deformation, in conjunction with pulseheating from the heaters 218, form metal-to-metal bonds between thejoining surfaces 216 and the joining surface material 222.

FIG. 12 illustrates another embodiment of a hermetic seal system 230having heaters 234. In FIG. 12, the second substrate 232 material is thestructural core 233 of the joint structures, which comprise structuralcore 233, the heaters 234, the intermediate layers 236, and the joiningsurface material 238. In contrast, FIG. 11 illustrates an embodiment inwhich the heaters 218 and intermediate layers 220 form the core of thejoint structure. Thus, the joint structure on second substrate 232 inFIG. 12 can be more rigid than the joint structure on second substrate212 in FIG. 11. Consequently, more local deformation at the joiningsurfaces may occur in hermetic seal system 230 during thermocompressionbonding. It should be understood that this increased rigidness in thejoint structures is also dependant upon the specific materials selected.

FIG. 13 illustrates an embodiment of a hermetic seal system 240 havingheaters 244 in contact with the joining surface material 246. FIG. 14illustrates another embodiment of a hermetic seal system 250 havingheaters 254 in contact with the joining surface material 256. In FIG.14, the joint structure cores on the second substrate 252 comprisesubstrate material and may be a stiffer joint structure than the jointstructures on the second substrate 242 in FIG. 13, which do not comprisesubstrate material. The joining surface materials 246 and 256 may beheated primarily from the heaters 244 and 254 underneath. In analternate embodiment, the joining surface material may be heateddirectly by passing a current through the joining surface.

It should be understood that the embodiments illustrated in FIGS. 11-14may have a first substrate and second substrate comprising differentmaterials. In addition, the joint structures of the first substrate maycomprise the same material or a different material than the joiningsurfaces of the first substrates and the joining surfaces of the secondsubstrates. Furthermore, the joining surfaces on the first substratesand the joining surfaces on the second substrates may comprise the samematerial or different materials. The joining surfaces of the secondsubstrates and the heaters may comprise the same material or differentmaterials. In addition, the bonding surface may melt during the pulsedheating, as would be the case in soldering processes.

Minimization of the Mechanical Force Required for Cold Welding

Minimization of the mechanical force required to bond the substrates canreduce the risk of damaging the substrate or substrate coatings.Minimizing the mechanical force required can be accomplished by variousmethods. These methods include various joint structure designs, joiningsurface material selections, joining surface material processingprocedures, and cold welding process parameters.

For example, the total amount of interference or overlap between thesealing features is governed by the joint structure design. A greateroverlap or interference between mating joint structures requires alarger force to cold weld, since a larger volume of metal is beingdeformed during the cold welding process. Therefore, to minimize theforce required, the total amount of metal deformed should be minimized.This can be accomplished by minimizing the shear layer or interface ofthe joining surface and also minimizing the amount of interferencebetween joint structures. Preferably, the overlap would be just slightlylarger than the joint structure tolerances, surface roughness, andassembly equipment accuracy tolerance. Additionally, by creating onlyone shear layer (as shown in FIG. 2) the force required can besignificantly reduced.

In addition, the use of various combinations of joint structurecross-section geometries allow for the optimization of the hermetic sealfor specific applications. For example, a combination of arectangular-shaped tongue joint structure joined together with atrapezoidal-shaped groove joint structure decreases the area in whichthe joining surfaces meet. In this embodiment, only the corners of therectangular joint structure initiate shear. The initial area of localshear is much smaller than in an embodiment having a rectangular-shapedtongue joint structure and a rectangular-shaped groove joint structure.Thus, the force required to cold weld is reduced.

In another embodiment, the required force is reduced further if only onecorner of the rectangular tongue joint structure initiates a shear forcewith the sloped trapezoidal groove joint structure. The force requiredto initiate plastic deformation on one corner of the rectangular tongueis half the force required to create the same pressure on two corners ofthe rectangular tongue.

In addition to joint design, the joining surface material compositionand associated physical properties can have an effect on the forcerequired to form the hermetic seal. For example, a joining structurematerial can have a low yield stress, which consequently makes thematerial easier to deform and makes it easier to expose clean bondablesurfaces. Suitable joining surface materials with low yield stressesinclude, but are not limited to, indium, aluminum, gold, and tin.Conversely, impurities will act to increase the yield stress of thebasic metal either by adding strain energy to the crystal structure orinterfering with dislocation mobility. Therefore, increasing thematerial purity can reduce the yield stress. Exceptions may exist wherethe addition of a second material may lower the melting point and thusthe overall yield stress is reduced because the ambient temperature iscloser to the melting point.

Another physical property which affects the force required for coldwelding is the hardness of a joining surface metal's oxide. Metalshaving a higher ratio between the oxide hardness and parent metalhardness require less deformation to cold weld. Conversely, soft metaloxides deform with the parent metal and do not fracture as easily thusmaintaining the oxide barrier to cold weld bonding. Metals having a highoxide to parent metal hardness ratio include, but are not limited to,indium and aluminum. Since gold and platinum do not have an oxide underambient conditions, the oxide hardness to parent metal hardness does notsubstantially affect the amount of force required to cold weld thesemetals. However, gold and platinum do have an adsorbed organiccontaminant layer that acts as a barrier to cold weld bonding.

Furthermore, a joining surface metal's grain structure and inherentstrain influence the yield strength. In polycrystalline metals, theyield stress is often described by the Hall-Petch relationship where theyield stress scales as one over the square root of the grain size. Thisrelationship exists because the crystallographic slip plane in adjacentgrains do not usually line up, so additional stress is required toactivate a new slip plane in the adjacent grain. Therefore, bydecreasing the number of grains (i.e., increasing the grain size) theyield stress can be lowered. Annealing the metal can lower the yieldstress by increasing the grain size and decreasing the inherent strainin the metal. Annealing may also have other beneficial effects such asdesorbing entrapped hydrogen from electroplated layers.

Finally, the bonding process can influence the force required to formthe hermetic seal. In addition, minimizing the total amount ofdeformation will reduce the amount of strain hardening the joiningsurface material develops. For instance, shorter joint structures maydevelop less strain hardening since the total amount of deformation isreduced. In addition, the cold welding process time or strain rate mayalso have an effect on the strain hardening. The bonding time also mayinfluence the amount of metal interdiffusion. See Takahashi & Matsusaka,“Adhesional bonding of fine gold wires to metal substrates,” J. AdhesionSci. Technol., 17(3):435-51 (2003).

In sealing with a compression force, it may be desirable to align thesupport force with the compressive force, in order to avoid a cantilevertype force on one of the substrates that might result in fracture ofsome substrate materials. In one embodiment, this may be accomplished byinserting a first substrate, which is to be protected from thecompression forces, within at least two other substrate structures,which are then sealed together, e.g., by cold welding as describedherein. In a preferred embodiment, at least one of the two othersubstrate structures includes a cavity or recess suitable for cradlingor otherwise holding the first substrate. The at least two othersubstrate structures have joint structures which can be compressedtogether to trap the first substrate in a cavity defined between the atleast two other substrate structures. FIG. 22 illustrates one embodimentof such as sealing approach. Sealed device 500 includes a sensorsubstrate 506 which has fabricated thereon a biosensor 508. The sensorsubstrate is placed in cavity 505 in base substrate 502. Upper substrate504, which includes reservoir caps/openings 512, is bonded to basesubstrate 502 by a compression cold welding process applied at jointstructures 510. In another embodiment, the third, or “sensor,” substratehas a different secondary device on it, instead of a sensor. Forexample, the third substrate may include a MEMS device, such as agyroscope, resonator, etc. The device could be sealed under vacuum.

Compressed Gasket Approach

In another aspect, a compression seal is formed in the absence ofmetal-to-metal bonding. In this case, the parts may require a permanentjoining force to remain hermetic. The joining force can be appliedthrough a variety of clamping mechanisms. In one embodiment, a Nitinol,or other shape memory alloy, clamp can be fashioned to provide a loosefit around the substrates until they are aligned, after which theNitinol can be heated past its phase transition point causing it toclamp down onto the substrates as shown in FIG. 15. This phasetransition temperature can be controlled (by varying the composition ofthe shape memory alloy). Therefore, device assembly can occur atsub-phase transition temperatures, then the assembly is warmed to thephase transition temperature and the clamping mechanism is activated.

In another embodiment, a metal or plastic clamp can be elasticallydeformed to allow the substrates of a hermetic seal system to be mountedwhere the clamp's zero stress configuration is significantly smallerthan the joining substrates. Once the joining substrates are alignedbetween the clamp, all forces on the clamp can be removed allowing it tosqueeze the joining substrates. Other fasteners including screws,rivets, solders, heat shrinking polymers, opposed magnets, and the like,can be fashioned to clamp the substrates. The clamp should be able topermanently apply a force while minimizing the additional size of thejoining pair.

An embodiment of a hermetic seal system 270 having a solder clamp isillustrated in FIGS. 16A-C. In FIG. 16A, the hermetic seal system 270comprises posts 276 which are attached, plated or micro-machined onto asecond substrate 274. Solder 278 is patterned on top of the posts 276.Second joint structures 280 on the second substrate 274 are aligned tooverlap a groove joint structure 282 on the first substrate 272. Pads284 comprising metal are deposited onto the top of the first substrate272. A heater plate 286 containing heaters 288 is aligned with thesolder 278 on top of the posts 276 and overlapping onto the metal pads284 on the first substrate 272.

As illustrated in FIG. 16B, the heater plate 286 presses the first andsecond substrates 272 and 274 together, creating a seal between thefirst joint structures 280 and the overlapping groove joint structure282. As the heater plate 286 presses down, the heaters 288 are pulsed toreflow the solder 278 so that the solder reflows onto the metal pads 284on the first substrate 272. The heater plate 286 may then be removedonce the solder 278 solidifies. FIG. 16C illustrates the hermetic sealsystem 270 after removal of the heater plate 286 and after formation ofthe solder clamp and hermetic seal.

In an alternate embodiment (not shown), the heater plate 286 may becoated with materials that can tolerate the heater temperature used andthat act as a poor surface for the solder 278 to bond to, depending onthe solder used. In such an embodiment, the heater plate 286 may beremoved once the solder 278 solidifies without the solder bonding to theheaters 288. In addition, the thickness of reflowed solder 278 onto themetal pads 284 may be adjusted depending on the desired strength of thesolder clamp.

The cold welding sealing features of the present invention may also beemployed to form a clamp for a compressive hermetic seal. FIG. 17illustrates an embodiment of a hermetic seal system 290 where a tongueand groove joint structure design is used to clamp a compression sealmaterial 306 between two substrates 292 and 294 and create a compressionhermetic seal. The first joint structure 296 a/296 b comprises thegroove portion of the joint structure design. The tongue portion of thejoint structure design comprises a heater 300 on the second substrate294, a intermediate layer 302 on the heater, and a joining surfacematerial 304 on the intermediate layer. The compression seal material306 has a round cross-section and is disposed on the second substrate294 between the tongue and groove clamp at the edge of the substrates.The groove joint structure of the first substrate 292 is then joined tothe tongue joint structure of the second substrate 294 usingthermocompression bonding, clamping the compression seal materialbetween the substrates and forming a hermetic seal. It should be clearthat any of the features described for cold welding may be used tocreate a cold weld clamp without the addition of heat. A cold weld clampwould not have the requirement of a closed geometry since its mainfunction is to clamp two substrates together, not create a seal.

In another embodiment (not shown), the compression seal material may bedisposed on the second substrate on the edges of the second substrate,outside the tongue and groove clamp. It should be understood however,that the stresses on the substrate materials will differ depending onthe placement of the compression seal material.

Depending on the application, compliant polymers may replace any of themetal joint structures and joining surfaces in the embodiments describedabove. Although the sealing mechanism for sealing compliant polymers isnot defined as cold welding, the effect of isolating a reservoir orcavity from adjacent cavities or external contamination with seals isthe same. Compliant polymers can require significantly less pressure tocreate a seal than the pressure required to create plastic deformationin a cold weld process. Traditionally compliant polymers have been poorchoices to seal in applications where water permeation is critical.However, recent advances in polymer chemistry have produced polymersthat have been modified to significantly reduce water permeation by theaddition of metal, or ceramic particles. For example, an epoxy modifiedby the addition of carbon nanoparticles has a reported water permeationrate an order of magnitude lower than conventional epoxies. Compliantpolymer seals require selection of low Young's modulus polymers andminimization of the surface contact area to provide seals using lowcompressive forces. In addition, increasing the number of circumscribedjoint structures may create pockets which act to significantly slowwater permeation through the seals.

The above described embodiments and examples can be practiced using asingle joint structure design or multiple redundant, joint structures tomitigate potential fabrication defects that may result in one or more ofthe redundant joint structures leaking. Additionally, multiple joiningsurfaces act to increase the seal path length and therefore increase theforce required to form a seal. The number of redundant joint structuresneeds to be balanced with the strength of the substrate materials, theforce required to cold weld them, and any residual stresses that remainin the substrate after the cold weld process, including stresses appliedby any clamping features.

Applications of the Hermetically Sealed Devices and Methods

The cold welding technique has a number of advantages in terms of bothprocessing and manufacturability. First, the sealing features areamenable to standard MEMs processes and can be incorporatedmonolithically into the MEMs device. Second, an array of closely spacedreservoirs can be sealed simultaneously. In fact, entire wafers ofdevices can be sealed simultaneously in a wafer-to-wafer bondingprocess. Multiple wafers can be sequentially or simultaneously bondedone on top of the other so that a cold weld is made on each surface ofthe internal wafers. In addition, active devices can be integrated withpassive devices by passing feed-throughs under the sealing features.Finally, since the process does not involve heat, temperature sensitivematerials can be packaged in the reservoir volume. Temperature sensitivematerials may include volatile liquids, organic chemicals, drugs,explosive gases, chemical sensors, and sensitive electronics.

FIG. 18 illustrates an embodiment of active and passive wafers coldwelded together to form an array of hermetically sealed devices 310. Thearray of hermetically sealed devices 310 represents one die that wascold welded simultaneously as part of an array of die on the same wafer.A first active layer 312 comprises sensors 320, a gold electrical tracelayer 322, dielectric layers 318, and tongue joint structures 324.Dielectrics between the active layer substrates and any electrical tracelayers are omitted for simplicity. These tongue joint structures 324comprise gold and are cold welded to a passive layer 314 having a groovejoint structures into which the first tongue joint structures arecompressed. The passive layer 314 comprises a metallization layer havingsecond tongue joint structures 326 and openings which are aligned withthe sensors 320 on the first active layer 312. The second tongue jointstructures 326 are cold welded to a groove joint structure in a secondactive layer 316. The second active layer comprises openings which arealigned with the sensors 320 on the first active layer. In addition, thesecond active layer comprises a metallization layer having reservoircaps 328. Thus, the array of hermetically sealed devices 310, asillustrated in FIG. 18 has separated the sensors 320 from each other andfrom the environment with hermetic seals. However, the reservoir caps328 may be later opened to expose the sensors 320 to the environment.Electrical connections to the active component 320 may be achieved usingvias depending upon the substrate material and fabrication limitations.

FIG. 19 illustrates a perspective view of an embodiment of amulti-reservoir drug delivery chip having an first active layer 332, apassive layer 334, and a second active layer 336. Layers 332 and 334,which are shown separated to illustrate the joint structures on layer332, are (to be) bonded by compression cold welding. (Layers 334 and 336need not be bonded by any particular technique.)

In an implanted medical sensor application, a compliant polymer may bepatterned on each substrate. The polymer can be patterned usingconventional MEMs techniques such as molding (e.g., PDMS softlithography), photolithography (e.g., photo-definable silicone),stereolithography, selective laser sintering, inkjet printing,deposition and reflowed, or etched (e.g., O₂ plasma etching).Alternatively, the polymer can be patterned and metallized prior toplacing it in between the opposing substrate.

FIG. 20 illustrates various embodiments of hermetic seal systems havingvarious polymer joint structures 346, 350, 366, 370, 382 with adeposited metal joining surfaces 348, 352, 368, 372, 383, 388, 392. Inthis case, metal-metal bonds are not formed by shear deformation, but bythe mechanism detailed in Ferguson et al. Hermetic seal system 340maximizes the contact area and leak path length. Hermetic seal system360 minimizes the contact area to increase the local pressure whendisplacing the surface contaminants during cold welding. Hermetic sealsystem 380 comprises a polymer pre-form 382 that is not fabricated ontoa substrate. The pre-form includes a metallized surface 383. Hermeticseal system 380 may be characterized as a metallized gasket seal system.

In certain embodiments, acoustic (e.g., ultrasound) or laser energy canbe used in a process to bond a metal with a polymer. This application ofacoustic or laser energy can be applied to methods which bond a metallayer/coating onto a polymeric substrate, or alternatively, bond apolymeric coating/layer onto a metal substrate. Examples of polymericmaterials in these embodiments include fluoropolymers, such as expandedpolytetrafluoroethylene (ePTFE), or a liquid crystalline polymer. In oneembodiment, a liquid crystalline polymeric substrate (e.g., certainhermetic LC polyesters) is bonded to another liquid crystallinepolymeric substrate, or it is metallized and the metallized surface isbonded to another liquid crystalline polymeric substrate or anothermetallized surface.

In further or alternative embodiments, the sealing concepts described inU.S. Patent Application Publication No. 2002/0179921 A1 to Cohn can beadapted for use in the hermetic sealing of implantable drug delivery oranalyte sensing applications described herein and in U.S. Pat. Nos.5,797,898, 6,527,762, 6,491,666, and 6,551,838, and U.S. PatentApplication Publication Nos. 2004/0121486 A1, 2004/0127942 A1, and2004/0106953 A1.

The devices described herein can be used with or incorporated into avariety of devices, including implantable medical devices and otherdevices. Examples include drug delivery devices, diagnostic and sensingdevices, some of which are described in U.S. Pat. No. 5,797,898,6,551,838, 6,527,762, as well as in U.S. Patent Application PublicationsNo. 2002/0099359, No. 2003/0010808, No. 2004/0121486, which areincorporated herein by reference.

FIG. 21 illustrates a cross-sectional view of one embodiment of amicrochip device before and after the open reservoirs are sealed usingcold welding. Device substrate 402 has reservoirs 404, loaded withreservoir contents 406. The reservoirs 404 are closed off on the frontside 401 of the substrate 402 by reservoir caps 408. The back sidesurface of the substrate 402 has one tongue joint structure 414 on eachside of each reservoir 404. A sealing substrate 410 is positioned overthe back side 403 of the device substrate 402 over the open reservoirs404. The sealing substrate 410 has groove joint structures 412 a/412 baligned to the tongue joint structures 414. The sealing substrate may betransparent to optical wavelengths from visible to infrared by selectingan appropriate material. In this way the reservoir contents may beoptically probed. The two substrates are then joined together and coldwelding at the tongue and groove joint structures 414/412 a and 412 bcreates hermetic seals separating the individual reservoirs 404 from oneanother and from the environment.

In some embodiments, the hermetically sealed device described herein isa subcomponent of another device. For example, it may be part of animplantable drug delivery device that further comprises a sensorindicative of a physiological condition of a patient, an electrode forproviding electrical stimulation to the body of a patient, a pump, acatheter, or a combination thereof. Examples of some of these aredescribed in U.S. Patent Application Publications No. 2004/0127942 A1and No. 2004/0106953 A1, and in U.S. Pat. No. 6,491,666, which areincorporated herein by reference.

Electrical Vias and Wire Connections Made by Compression Cold Welding

In another aspect, the compression cold welding techniques describedherein are adapted to create highly reliable, low resistance electricalconnections without heat. In one embodiment, the bond structure formedby compression cold welding provides simultaneously a mechanicalsecurement means and a continuous electrical conducting path.

One embodiment of an electrical via connection 600 is shown in FIG. 23.A first metal layer 602 on a first surface 604 of first substrate 618 isto be electrically connected to a second metal layer 606 on a surface608 of second substrate 609. Metal deposited on the inside of the sealfeature 610 on the first substrate creates electrical contact betweenthe first metal layer 602 and the first joining surface 612. The secondjoining surface 614 may be formed by electroplating a tooth 605 on thesecond metal layer 606. The width of the tooth exceeds the width of themetallized hole by between 1-50 um. The cross section of the sealstructure 610 through substrate 604 is shown to be rectangular, but itmay be any shape that can be fabricated using micromachining or MEMsprocesses to maximize coverage of deposited material and reduce residualstresses in the joint. When the joining surfaces 612 and 614 are alignedand the substrates 618 and 609 are compressed together, shear at thejoining interface exposes clean metal on both joining surfaces, creatinga cold weld bond. The resulting bond creates a low resistance electricalconnection between the first metal layer 602 and the second metal layer606.

It should be understood that this technique is not limited to anelectroplated ridge of a particular metal or alloy or shape. The ridgecross-section in the plating direction may be rectangular (as shown),hemispherical, triangular, trapezoidal—any shape appropriate to create acold weld joint as described herein. Any of the conductive materialsdescribed herein may be considered for use as joining materialsincluding metals or conductive polymers with appropriate mechanical andelectrical properties to create electrical connection by elasticcompression rather than cold welding. The second joining structure mayhave a core that is a different material than, or the same as, thematerial of the joining surface. All the sealing features describedherein for creating cold weld joints may be used to create electricalconnections as well.

Multiple electrical connections may be created in a small area usingtraditional MEMS processes and/or micromachining to deposit and patternmetal and to create vias through the substrates. The electricalconnection features described herein may be included on substrates withseal features such that the electrical connections are createdsimultaneously with the hermetic seal when two opposing substrates arecompressed together.

In another embodiment, it may be advantageous to have sloped side wallson the first joining surface 612 to more easily accommodate depositionof the first joint surface 612. Furthermore, material deposition mayoccur on both sides 616 and 618 of the first substrate 604. This is onemethod of ensuring proper material deposition throughout the via hole607.

FIGS. 25 and 26 further illustrate possible embodiments for electricalvias made by compression cold welding.

One embodiment of an electrical wire connection 700 is shown in FIGS.24A-B. Conductive leads 702 a, 702 b are to be electrically connected totraces 704 a, 704 b, respectively, on substrate 706. Each conductivelead 702 a, 702 b has a diameter greater than joining surface widths 708a, 708 b and are aligned and pressed into seal features 710 a, 710 b.Seal features 710 a, 710 b may be formed by etching trenches intosubstrate 706 and then depositing a metal layer 704 a, 704 b in them.The trenches are wider at one end, which provides space to appropriatelyrelieve strain in the conductive leads 702 a, 702 b using epoxy,silicone, solder, or other polymeric material. The space also allows theleads to lay parallel to the top surface of substrate 706 even though asmaller area of the trench is used to create the cold weld to theconductive leads.

The leads are shown having a circular cross section; however, anycross-section suitable to forming a cold weld or compressive seal asdescribed herein may be used. The cross section of the seal structures710 a, 710 b through substrate 710 a, 710 b is shown to be rectangular,but it may be any shape that can be fabricated using micromachiningprocesses or MEMs processes to maximize coverage of deposited materialand reduce residual stresses in the joint.

In alternative embodiments, electrical connections may be created usingthe elastic properties of the conductive leads and/or the conductivelayers 704 a, 704 b rather than a cold weld to cause a press fit orfriction fit capture.

The conductive leads may be formed of a single material, multiple layersof different materials, and/or coated with an electrical insulationlayer. Local shear may sufficiently deform the insulation layer toexpose the conductive leads underneath and create a cold weld orcompressive electrical connection.

In alternate embodiments, non-metal conductive materials, such as asilver impregnated polymer, may be used in place of metal layers in thevia or wire connections described above. In a preferred embodiment, thematerials of construction are biocompatible and biostable.

Further Details of the Multi-Cap Reservoir Devices

Substrate and Reservoirs

In one embodiment, the containment device comprises a body portion,i.e., a substrate, that includes one or more reservoirs for containingreservoir contents sealed in a fluid tight or hermetic manner. As usedherein, the term “hermetic” refers to a seal/containment effective tokeep out helium, water vapor, and other gases. As used herein, the term“fluid tight” refers to a seal/containment which is not gas hermetic,but which are effective to keep out dissolved materials (e.g., glucose)in a liquid phase. The substrate can be the structural body (e.g., partof a device) in which the reservoirs are formed, e.g., it contains theetched, machined, or molded reservoirs.

In preferred embodiments, the reservoirs are discrete, non-deformable,and disposed in an array across one or more surfaces (or areas thereof)of the device body. As used herein, the term “reservoir” means a well, acavity, or a hole suitable for storing, containing, andreleasing/exposing a precise quantity of a material, such as a drugformulation, or a secondary device, or subcomponent. The interconnectedpores of a porous material are not reservoirs. In a one embodiment, thedevice includes a plurality of the reservoirs located in discretepositions across at least one surface of the body portion. In anotherembodiment, there is a single reservoir per each reservoir substrateportion; optionally two or more of these portions can be used togetherin a single device.

Reservoirs can be fabricated in a structural body portion using anysuitable fabrication technique known in the art. Representativefabrication techniques include MEMS fabrication processes,microfabrication processes, or other micromachining processes, variousdrilling techniques (e.g., laser, mechanical, and ultrasonic drilling),and build-up or lamination techniques, such as LTCC (low temperatureco-fired ceramics). The surface of the reservoir optionally can betreated or coated to alter one or more properties of the surface.Examples of such properties include hydrophilicity/hydrophobicity,wetting properties (surface energies, contact angles, etc.), surfaceroughness, electrical charge, release characteristics, and the like.MEMS methods, micromolding, micromachining, and microfabricationtechniques known in the art can be used to fabricate thesubstrate/reservoirs from a variety of materials. Numerous other methodsknown in the art can also be used to form the reservoirs. See, forexample, U.S. Pat. No. 6,123,861 and U.S. Pat. No. 6,808,522. Variouspolymer forming techniques known in the art also may be used, e.g.,injection molding, thermocompression molding, extrusion, and the like.

In various embodiments, the body portion of the containment devicecomprises silicon, a metal, a ceramic, a polymer, or a combinationthereof. Examples of suitable substrate materials include metals (e.g.,titanium, stainless steel), ceramics (e.g., alumina, silicon nitride),semiconductors (e.g., silicon), glasses (e.g., Pyrex™, BPSG), anddegradable and non-degradable polymers. Where only fluid tightness isrequired, the substrate may be formed of a polymeric material, ratherthan a metal or ceramic which would typically be required for gashermeticity.

In one embodiment, each reservoir is formed of (i.e., defined in)hermetic materials (e.g., metals, silicon, glasses, ceramics) and ishermetically sealed by a reservoir cap. Desirably, the substratematerial is biocompatible and suitable for long-term implantation into apatient. In a preferred embodiment, the substrate is formed of one ormore hermetic materials. The substrate, or portions thereof, may becoated, encapsulated, or otherwise contained in a hermetic biocompatiblematerial (e.g., inert ceramics, titanium, and the like) before use.Non-hermetic materials may be completely coated with a layer of ahermetic material. For example, a polymeric substrate could have a thinmetal coating. If the substrate material is not biocompatible, then itcan be coated with, encapsulated, or otherwise contained in abiocompatible material, such as poly(ethylene glycol),polytetrafluoroethylene-like materials, diamond-like carbon, siliconcarbide, inert ceramics, alumina, titanium, and the like, before use. Inone embodiment, the substrate is hermetic, that is impermeable (at leastduring the time of use of the reservoir device) to the molecules to bedelivered and to surrounding gases or fluids (e.g., water, blood,electrolytes or other solutions).

The substrate can be formed into a range of shapes or shaped surfaces.It can, for example, have a planar or curved surface, which for examplecould be shaped to conform to an attachment surface. In variousembodiments, the substrate or the containment device is in the form of aplanar chip, a circular or ovoid disk, an elongated tube, a sphere, or awire. The substrate can be flexible or rigid. In various embodiments,the reservoirs are discrete, non-deformable, and disposed in an arrayacross one or more surfaces (or areas thereof) of an implantable medicaldevice.

The substrate may consist of only one material, or may be a composite ormulti-laminate material, that is, composed of several layers of the sameor different substrate materials that are bonded together. Substrateportions can be, for example, silicon or another micromachined substrateor combination of micromachined substrates such as silicon and glass,e.g., as described in U.S. Patent Application Publication 2005/0149000or U.S. Pat. No. 6,527,762. In another embodiment, the substratecomprises multiple silicon wafers bonded together. In yet anotherembodiment, the substrate comprises a low-temperature co-fired ceramic(LTCC) or other ceramic such as alumina. In one embodiment, the bodyportion is the support for a microchip device. In one example, thissubstrate is formed of silicon.

In one embodiment, either or both substrates to be bonded may be formedof one or more glasses, which may be particularly useful in embodimentswhere it is desirable to view or interrogate an object or material thatis contained between the sealed substrates, e.g., in a cavity orreservoir. That is, where the substrate can serve as an fluid-tightwindow. Representative examples of glasses include aluminosilicateglass, borosilicate glass, crystal glasses, etc.

Total substrate thickness and reservoir volume can be increased bybonding or attaching wafers or layers of substrate materials together.The device thickness may affect the volume of each reservoir and/or mayaffect the maximum number of reservoirs that can be incorporated onto asubstrate. The size and number of substrates and reservoirs can beselected to accommodate the quantity and volume of reservoir contentsneeded for a particular application, manufacturing limitations, and/ortotal device size limitations to be suitable for implantation into apatient, preferably using minimally invasive procedures.

In a preferred embodiment for an implantable sensor application using aplanar sensor, the substrate preferably is relatively thin, as notedabove.

The substrate can have one, two, three or more reservoirs. In variousembodiments, tens, hundreds, or thousands of reservoirs are arrayedacross the substrate. For instance, one embodiment of an implantabledrug delivery device includes between 250 and 750 reservoirs, where eachreservoir contains a single dose of a drug for release. In one sensingembodiment, the number of reservoirs in the device is determined by theoperation life of the individual sensors. For example, a one-yearimplantable glucose-monitoring device having individual sensors thatremain functional for 30 days after exposure to the body would containat least 12 reservoirs (assuming one sensor per reservoir). In anothersensor embodiment, the distance between the sensor surface and thereservoir opening means is minimized, preferably approaching a fewmicrons. In this case, the volume of the reservoir is primarilydetermined by the surface area of the sensor. For example, theelectrodes of a typical enzymatic glucose sensor may occupy a space thatis 400 μm by 800 μm.

In one embodiment, the reservoirs are microreservoirs. The“microreservoir” is a reservoir suitable for storing andreleasing/exposing a microquantity of material, such as a drugformulation. In one embodiment, the microreservoir has a volume equal toor less than 500 μL (e.g., less than 250 μL, less than 100 μL, less than50 μL, less than 25 μL, less than 10 μL, etc.) and greater than about 1nL (e.g., greater than 5 nL, greater than 10 nL, greater than about 25nL, greater than about 50 nL, greater than about 1 μL, etc.). The term“microquantity” refers to volumes from 1 nL up to 500 μL. In oneembodiment, the microquantity is between 1 nL and 1 μL. In anotherembodiment, the microquantity is between 10 nL and 500 nL. In stillanother embodiment, the microquantity is between about 1 μL and 500 μL.The shape and dimensions of the microreservoir can be selected tomaximize or minimize contact area between the drug material (or sensoror other reservoir contents) and the surrounding surface of themicroreservoir.

In one embodiment, the reservoir is formed in a 200-micron thicksubstrate and has dimensions of 1.5 mm by 0.83 mm, for a volume of about250 nL, not counting the volume that would be taken up by the supportstructures, which may be about 20 to about 50 microns thick.

In another embodiment, the reservoirs are macroreservoirs. The“macroreservoir” is a reservoir suitable for storing andreleasing/exposing a quantity of material larger than a microquantity.In one embodiment, the macroreservoir has a volume greater than 500 μL(e.g., greater than 600 μL, greater than 750 μL, greater than 900 μL,greater than 1 mL, etc.) and less than 5 mL (e.g., less than 4 mL, lessthan 3 mL, less than 2 mL, less than 1 mL, etc.).

Unless explicitly indicated to be limited to either micro- ormacro-scale volumes/quantities, the term “reservoir” is intended toencompass both.

In one embodiment, the device comprises a microchip chemical deliverydevice. In another embodiment, the device includes polymeric chips ordevices composed of non-silicon based materials that might not bereferred to as “microchips.” In one embodiment, the device comprises anosmotic pump, for example, the DUROS™ osmotic pump technology (AlzaCorporation) included in commercial devices such as a VIADUR™ implant(Bayer Healthcare Pharmaceuticals and Alza Corporation).

Reservoir Cap Supports

Reservoir cap supports can comprise substrate material, structuralmaterial, or coating material, or combinations thereof. Reservoir capsupports comprising substrate material may be formed in the same step asthe reservoirs. The MEMS methods, microfabrication, micromolding, andmicromachining techniques mentioned above could be used to fabricate thesubstrate/reservoirs, as well as reservoir cap supports, from a varietyof substrate materials. Reservoir cap supports comprising structuralmaterial may also be formed by deposition techniques onto the substrateand then MEMS methods, microfabrication, micromolding, andmicromachining techniques. Reservoir cap supports formed from coatingmaterial may be formed using known coating processes and tape masking,shadow masking, selective laser removal techniques, or other selectivemethods.

A reservoir may have several reservoir cap supports in variousconfigurations over its reservoir contents. For example, one reservoircap support may span from one side of the reservoir to the oppositeside; another reservoir cap support may cross the first reservoir capsupport and span the two other sides of the reservoir. In such anexample, four reservoir caps could be supported over the reservoir.

In one embodiment for a sensor application (e.g., a glucose sensor), thereservoir (of a device, which can include only one or which may includetwo or more reservoirs) has three or more reservoir openings andcorresponding reservoir caps.

The dimensions and geometry of the support structure can be varieddepending upon the particular requirements of a specific application.For instance, the thickness, width, and cross-sectional shape (e.g.,square, rectangular, triangular) of the support structures may betailored for a particular drug release kinetics for a certain drugformulation or implantation site, etc.

Reservoir Contents

The reservoir contents are essentially any object or material that needsto be isolated (e.g., protected from) the environment outside of thereservoir until a selected point in time, when its release or exposureis desired. In various embodiments, the reservoir contents comprise (aquantity of) chemical molecules, a secondary device, or a combinationthereof.

Proper functioning of certain reservoir contents, such as a catalyst orsensor, generally does not require release from the reservoir; rathertheir intended function, e.g., catalysis or sensing, occurs uponexposure of the reservoir contents to the environment outside of thereservoir after opening of the reservoir cap. Thus, the catalystmolecules or sensing component can be released or can remain immobilizedwithin the open reservoir. Other reservoir contents such as drugmolecules often may need to be released from the reservoir in order topass from the device and be delivered to a site in vivo to exert atherapeutic effect on a patient. However, the drug molecules may beretained within the reservoirs for certain in vitro applications.

In several embodiments, hermeticity, which is typically defined as amaximum allowable transport rate of a particular molecule (such ashelium or water) for a particular application, of the sealed reservoirsis required. That is, whether a reservoir is considered hermetic canvary among different applications of the device depending upon theparticular demands of the application.

Chemical Molecules

The reservoir contents can include essentially any natural or synthetic,organic or inorganic molecules or mixtures thereof. The molecules may bein essentially any form, such as a pure solid or liquid, a gel orhydrogel, a solution, an emulsion, a slurry, a lyophilized powder, or asuspension. The molecules of interest may be mixed with other materialsto control or enhance the rate and/or time of release from an openedreservoir.

In a preferred embodiment, the reservoir contents comprise a drugformulation. The drug formulation is a composition that comprises adrug. As used herein, the term “drug” includes any therapeutic orprophylactic agent (e.g., an active pharmaceutical ingredient or API).In one embodiment, the drug is provided in a solid form, particularlyfor purposes of maintaining or extending the stability of the drug overa commercially and medically useful time, e.g., during storage in a drugdelivery device until the drug needs to be administered. The solid drugmatrix may be in pure form or in the form of solid particles of anothermaterial in which the drug is contained, suspended, or dispersed. In oneembodiment, the drug is a protein or a peptide. Examples includeglycoproteins, enzymes (e.g., proteolytic enzymes), hormones or otheranalogs antibodies (e.g., anti-VEGF antibodies, tumor necrosis factorinhibitors), cytokines (e.g., α-, β-, or γ-interferons), interleukins(e.g., IL-2, IL-10), and diabetes/obesity-related therapeutics (e.g.,insulin, exenatide, PYY, GLP-1 and its analogs). The reservoirs in onedevice can include a single drug or a combination of two or more drugformulations. Different formulations can be stored together and releasedfrom the same one or more reservoirs or they can each be stored in andreleased from different reservoirs.

For in vitro applications, the chemical molecules can be any of a widerange of molecules where the controlled release of a small (milligram tonanogram) amount of one or more molecules is required, for example, inthe fields of analytic chemistry or medical diagnostics. Molecules canbe effective as pH buffering agents, diagnostic reagents, and reagentsin complex reactions such as the polymerase chain reaction or othernucleic acid amplification procedures. In other embodiments, themolecules to be released are fragrances or scents, dyes or othercoloring agents, sweeteners or other concentrated flavoring agents, or avariety of other compounds. In yet other embodiments, the reservoirscontain immobilized molecules. Examples include any chemical specieswhich can be involved in a reaction, including reagents, catalysts(e.g., enzymes, metals, and zeolites), proteins (e.g., antibodies),nucleic acids, polysaccharides, cells, and polymers, as well as organicor inorganic molecules which can function as a diagnostic agent.

The drug or other molecules for release can be dispersed in a matrixmaterial, to control the rate of release. This matrix material can be a“release system,” as described in U.S. Pat. No. 5,797,898, thedegradation, dissolution, or diffusion properties of which can provide amethod for controlling the release rate of the chemical molecules. Inone embodiment, the drug formulation within a reservoir comprises layersof drug and non-drug material. After the active release mechanism hasexposed the reservoir contents, the multiple layers provide multiplepulses of drug release due to intervening layers of non-drug. Such astrategy can be used to obtain complex release profiles. See also U.S.Patent Application Publication No. 2004/0247671 A1, which isincorporated herein by reference.

Secondary Devices

As used herein, unless explicitly indicated otherwise, the term“secondary device” includes any device or a component thereof that canbe located in a reservoir. In one embodiment, the secondary device is asensor or sensing component thereof. As used herein, a “sensingcomponent” includes a component utilized in measuring or analyzing thepresence, absence, or change in a chemical or ionic species, energy, orone or more physical properties (e.g., pH, pressure) at a site. Types ofsensors include biosensors, chemical sensors, physical sensors, oroptical sensors. Secondary devices are further described in U.S. Pat.No. 6,551,838. In one embodiment, the sensor is a pressure sensor. See,e.g., U.S. Pat. Nos. 6,221,024, and 6,237,398, and U.S. PatentApplication Publication No. 2004/0073137. Examples of sensing componentsinclude components utilized in measuring or analyzing the presence,absence, or change in a drug, chemical, or ionic species, energy (orlight), or one or more physical properties (e.g., pH, pressure) at asite. In still another embodiment, the sensor includes a cantilever-typesensor, such as those used for chemical detection. For example, see U.S.Patent Application Publication No. 2005/0005676, which is incorporatedherein by reference.

In a preferred embodiment, a device is provided for implantation in apatient (e.g., a human or other mammal) and the reservoir contentscomprise at least one sensor indicative of a physiological condition inthe patient. For example, the sensor could monitor the concentration ofglucose, urea, calcium, or a hormone present in the blood, plasma,interstitial fluid, vitreous humor, or other bodily fluid of thepatient.

In one embodiment, two bonded substrates include at least one cavity,which may be defined in one or both substrate portions, that contains aMEMS device. The MEMS device may be on a third substrate. The space inthe sealed cavity may be evacuated or may contain an inert gas or gasmixture (e.g., nitrogen, helium). The MEMS device may be one known inthe art, such as a pressure sensor, an accelerometer, a gyroscope, aresonator. In another embodiment, at least one of the bonded substratesis formed of a glass, and the cavity contains an optical sensor orchemical compound that can be optically interrogated.

Several options exist for receiving and analyzing data obtained withsecondary devices located within the primary device, which can be amicrochip device or another device. The primary devices may becontrolled by local microprocessors or remote control. Biosensorinformation may provide input to the controller to determine the timeand type of activation automatically, with human intervention, or acombination thereof. For example, the operation of the device can becontrolled by an on-board (i.e., within the package) microprocessor orstate machine. The output signal from the device, after conditioning bysuitable circuitry if needed, will be acquired by the microprocessor.After analysis and processing, the output signal can be stored in awriteable computer memory chip, and/or can be sent (e.g., wirelessly) toa remote location away from the microchip. Power can be supplied to themicrochip system locally by a battery or remotely by wirelesstransmission. See, e.g., U.S. Patent Application Publication No.2002/0072784.

In one embodiment, a device is provided having reservoir contents thatinclude drug molecules for release and a sensor/sensing component. Forexample, the sensor or sensing component can be located in a reservoiror can be attached to the device substrate. The sensor can operablycommunicate with the device, e.g., through a microprocessor, to controlor modify the drug release variables, including dosage amount andfrequency, time of release, effective rate of release, selection of drugor drug combination, and the like. The sensor or sensing componentdetects (or not) the species or property at the site of in vivoimplantation and further may relay a signal to the microprocessor usedfor controlling release from the device. Such a signal could providefeedback on and/or finely control the release of a drug. In anotherembodiment, the device includes one or more biosensors (which may besealed in reservoirs until needed for use) that are capable of detectingand/or measuring signals within the body of a patient. In one variation,an implantable medical device includes reservoirs comprising a sensor,sealed as described herein, and a signal from the sensor is transmitted(by any number of means, including hardwire or telemetry) to a separatedrug delivery device, which could be a wearable (i.e., external) orinternal pump, the signal being used in the control of the dosing of thedrug.

As used herein, the term “biosensor” includes sensing devices thattransduce the chemical potential of an analyte of interest into anelectrical signal (e.g., by converting a mechanical or thermal energyinto an electrical signal), as well as electrodes that measureelectrical signals directly or indirectly. For example, the biosensormay measure intrinsic electrical signals (EKG, EEG, or other neuralsignals), pressure, temperature, pH, or mechanical loads on tissuestructures at various in vivo locations. The electrical signal from thebiosensor can then be measured, for example by amicroprocessor/controller, which then can transmit the information to aremote controller, another local controller, or both. For example, thesystem can be used to relay or record information on the patient's vitalsigns or the implant environment, such as drug concentration.

In a preferred embodiment, the device contains one or more sensors foruse in glucose monitoring and insulin control. Information from thesensor could be used to actively control insulin release from the samedevice or from a separate insulin delivery device (e.g., a conventionalinsulin pump, either an externally worn version or an implantedversion). A hermetically sealed reservoir device may be provided in theform of an implantable multi-reservoir device storing an array ofglucose sensors and capable of transmitting (by wire or wirelessly)glucose readings to a handheld or worn glucose meter-type device, whichpermits the patient to manually administer insulin to themselves (e.g.,by injection). Other embodiments could sense other analytes and deliveryother types of drugs in a similar fashion.

Reservoir Caps

As used herein, the term “reservoir cap” refers to a membrane, thinfilm, or other structure suitable for separating the contents of areservoir from the environment outside of the reservoir, but which isintended to be removed or disintegrated at a selected time to open thereservoir and expose its contents. In a preferred embodiment, a discretereservoir cap completely covers one of the reservoir's openings. Inanother embodiment, a discrete reservoir cap covers two or more, butless than all, of the reservoir's openings. In preferred activelycontrolled devices, the reservoir cap includes any material that can bedisintegrated or permeabilized in response to an applied stimulus (e.g.,electric field or current, magnetic field, change in pH, or by thermal,chemical, electrochemical, or mechanical means). Examples of suitablereservoir cap materials include gold, titanium, platinum, tin, silver,copper, zinc, alloys, and eutectic materials such as gold-silicon andgold-tin eutectics. Any combination of passive or active barrier layerscan be present in a single device.

In one embodiment, the reservoir caps are electrically conductive andnon-porous. In a preferred embodiment, the reservoir caps are in theform of a thin metal film. In another embodiment, the reservoir caps aremade of multiple metal layers, such as a multi-layer/laminate structureof platinum/titanium/platinum. For example, the top and bottom layerscould be selected for adhesion layers on (typically only over a portionof) the reservoir caps to ensure that the caps adhere to/bonds with boththe substrate area around the reservoir openings, reservoir capsupports, and a dielectric overlayer. In one case, the structure istitanium/platinum/titanium/platinum/titanium, where the top and bottomlayers serve as adhesion layers, and the platinum layers provide extrastability/biostability and protection to the main, central titaniumlayer. The thickness of these layers could be, for example, about 300 nmfor the central titanium layer, about 40 nm for each of the platinumlayers, and between about 10 and 15 nm for the adhesion titanium layers.

Control Means for Disintegrating or Permeabilizing the Reservoir Cap

The containment device includes control means that facilitates andcontrols reservoir opening, e.g., for disintegrating or permeabilizingthe reservoir caps at a select time following sealing of the reservoirsas described herein. The control means comprises the structuralcomponent(s) and electronics (e.g., circuitry and power source) forpowering and for controlling the time at which release or exposure ofthe reservoir contents is initiated.

The control means can take a variety of forms. In one embodiment, thereservoir cap comprises a metal film that is disintegrated byelectrothermal ablation as described in U.S. Patent ApplicationPublication No. 2004/0121486 A1, and the control means includes thehardware, electrical components, and software needed to control anddeliver electric energy from a power source (e.g., battery, storagecapacitor) to the selected reservoir caps for actuation, e.g., reservoiropening. For instance, the device can include a source of electric powerfor applying an electric current through an electrical input lead, anelectrical output lead, and a reservoir cap connected therebetween in anamount effective to disintegrate the reservoir cap. Power can besupplied to the control means of the multi-cap reservoir system locallyby a battery, capacitor, (bio)fuel cell, or remotely by wirelesstransmission, as described for example in U.S. Patent ApplicationPublication No. 2002/0072784. A capacitor can be charged locally by anon-board battery or remotely, for example by an RF signal or ultrasound.

In one embodiment, the control means includes an input source, amicroprocessor, a timer, a demultiplexer (or multiplexer). The timer and(de)multiplexer circuitry can be designed and incorporated directly ontothe surface of the substrate during fabrication. In another embodiment,some of the components of the control means are provided as a separatecomponent, which can be tethered or untethered to the reservoir portionof the device. For instance, the controller and/or power source may bephysically remote from, but operably connected to and/or incommunication with, the multi-cap reservoir device. In one embodiment,the operation of the multi-cap reservoir system will be controlled by anon-board (e.g., within an implantable device) microprocessor. In anotherembodiment, a simple state machine is used, as it typically is simpler,smaller, and/or uses less power than a microprocessor.

Other reservoir opening and release control methods are described inU.S. Pat. Nos. 5,797,898, 6,527,762, and 6,491,666, U.S. PatentApplication Publication Nos. 2004/0121486, 2002/0107470 A1, 2002/0072784A1, 2002/0138067 A1, 2002/0151776 A1, 2002/0099359 A1, 2002/0187260 A1,and 2003/0010808 A1; PCT WO 2004/022033 A2; PCT WO 2004/026281; and U.S.Pat. Nos. 5,797,898; 6,123,861; and 6,527,762, all of which areincorporated by reference herein.

Using the Multi-Cap Reservoir Systems/Devices

The multi-cap reservoir release/exposure devices and systems describedherein can be used in a wide variety of applications. Preferredapplications include the controlled delivery of a drug, biosensing, or acombination thereof. In a preferred embodiment, the multi-cap reservoirsystem is part of an implantable medical device. The implantable medicaldevice can take a wide variety of forms and be used in a variety oftherapeutic and/or diagnostic applications. In one embodiment, thereservoirs store and release a drug formulation over an extended periodof time. In another embodiment, the store and contain a sensor forselective exposure, wherein the reservoirs are opened as needed(depending, for example, upon fouling of the sensor) or as dictated by apredetermined schedule. For example, the reservoirs could contain apressure sensor, a chemical sensor, or a biological sensor. In aparticular embodiment, the reservoirs comprise a glucose sensor, whichmay, for instance, comprise glucose oxidase immobilized on an electrodein the reservoir and coated with one or more permeable/semi-permeablemembranes. Because the enzyme could lose its activity when exposed tothe environment (e.g., the body) before its intended time of use, thesealed reservoir serves to protect the enzyme until it is needed.

In still other embodiments, the multi-cap reservoir systems and devicesdescribed herein are incorporated into a variety of other devices. Forexample, the hermetically sealed reservoirs could be integrated intoother types and designs of implantable medical devices, such as thecatheters and electrodes described in U.S. Patent ApplicationPublication No. 2002/0111601. In another example, it could beincorporated into another medical device, in which the present devicesand systems release drug into a carrier fluid that then flows to adesired site of administration, as illustrated for example in U.S. Pat.No. 6,491,666. The hermetically sealed reservoirs also could beincorporated into a drug pump, an inhaler or other pulmonary drugdelivery device.

The sealed devices described herein also have numerous in vitro andcommercial diagnostic applications. The devices are capable ofdelivering precisely metered quantities of molecules and thus are usefulfor in vitro applications, such as analytical chemistry and medicaldiagnostics, as well as biological applications such as the delivery offactors to cell cultures. In still other non-medical applications, thedevices are used to control release of fragrances, dyes, or other usefulchemicals.

Still other applications are described in U.S. Pat. Nos. 5,797,898;6,527,762; 6,491,666; and 6,551,838, and U.S. Patent ApplicationPublications 2002/0183721, 2003/0100865, 2002/0099359, 2004/0082937,2004/0127942, 2004/0121486, 2004/0106914, and 2004/0106953, all of whichare incorporated by reference herein.

Embodiments of the invention can further be understood with reference tothe following non-limiting examples.

Example 1: Tongue and Groove Hermetic Seal

A hermetic seal was made using a tongue and groove joint design. Theseal was made by a compression cold welding process. FIG. 3 shows an SEMof the seal. The substrates are silicon (top) and alumina (bottom). Themetals are gold (sputtered on silicon, sputtered then electroplated onalumina). The parts were bonded on an FC-150 flip chip aligner, which isa machine that provides accurate alignment in x, y, z and pitch, roll,and yaw. Once the parts were aligned, the FC-150 compressed the partstogether and the cold weld bond was formed.

Example 2: Variation of Feature Sizes and Metal Thickness Impact onHermeticity

Several different joint designs were fabricated, using different featuresizes and metal layer thicknesses. The joints were compression coldwelded, and the sealed joints were tested for leaks using either a dyepenetrant test or a He leak detector depending on the part geometry. Asshown in Table 1 below, the seal integrity was found to be independentof feature size and gold metal layer thickness over the ranges tested.Undetectable leak rates may leak below the leak detectors lower limit orless than 5e-11 atm*cc/sec.

TABLE 1 Comparison of Various Joint Seals-Leak Test Ridge Ridge JointJoint Surface Groove Width Height structure Metal Groove Groove MetalLeak (188) (190) Material Thickness Width Depth Thickness Overlap TestResults μm μm — μm μm μm μm μm — — 145 50 Gold — 135 50 10 21 Dye LeakTight penetrant 50 50 Silicon 7 80 50 7 2 Dye Leak Tight penetrant 60 50Gold — 46 50 1 14 He Leak Undetectable 60 50 Gold — 53 50 10 7 He LeakUndetectable 60 50 Gold — 50 50 1 10 He Leak Undetectable

Example 3: Array of Microfabricated Cavities Having Individual SealFeatures

Two silicon substrates were provided made with complementary cavitiesand seal features for compression cold welding. The seal featuresincluded ridges that were microfabricated onto/into one substrate, andmatching grooves that were microfabricated onto/into the othersubstrate. A shallow, wide cavity was formed inside each groove andinside each ridge. FIGS. 27A-B show the resulting substrates and sealfeatures.

Publications cited herein are incorporated by reference. Modificationsand variations of the methods and devices described herein will beobvious to those skilled in the art from the foregoing detaileddescription. Such modifications and variations are intended to comewithin the scope of the appended claims.

We claim:
 1. A method of forming an electrical via connectioncomprising: providing a first non-conductive substrate having anaperture therethrough, wherein the interior surface of said firstsubstrate defining said aperture comprises a layer of a firstelectrically conductive material; providing a second non-conductivesubstrate having a projecting member extending from a surface of saidsecond substrate, wherein said projecting member is formed of or coatedwith a layer of a second electrically conductive material; andcompressing the projecting member of said second substrate into theaperture of said first substrate, to locally plastically deform andshear the first and second electrically conductive materials, in anamount effective to form a cold weld and electrical connection betweenthe first and second electrically conductive materials.
 2. The method ofclaim 1, further comprising: before the step of compressing, aligningthe projecting member of said second substrate relative to the apertureof said first substrate so as to impart one or more overlaps of theprojecting member relative to the aperture.
 3. The method of claim 2,wherein the step of compressing comprises locally deforming and shearingthe projecting member at one or more interfaces created by the one ormore overlaps in an amount effective to plastically deform at least aportion of the projecting member into a space between the firstsubstrate and the second substrate outside the aperture.
 4. The methodof claim 1, wherein the first non-conductive substrate, the secondnon-conductive substrate, or both first and second non-conductivesubstrates comprise silicon.
 5. The method of claim 4, wherein the firstelectrically conductive material, the second electrically conductivematerial, or both electrically conductive materials comprise gold,indium, aluminum, copper, lead, zinc, nickel, silver, palladium,cadmium, titanium, tungsten, tin, and combinations thereof.
 6. Themethod of claim 2, wherein the one or more overlaps have a width ofbetween 1 μm and 50 μm.
 7. The method of claim 1, wherein the projectingmember is cylindrical.
 8. The method of claim 1, wherein the firstnon-conductive substrate is rigid.
 9. The method of claim 8, wherein thefirst non-conductive substrate comprises silicon.
 10. A method offorming an electrical via connection comprising: providing a firstnon-conductive substrate having an aperture therethrough, wherein theinterior surface of said first substrate defining said aperturecomprises a layer of a first electrically conductive material; providinga second non-conductive substrate having a projecting member extendingfrom a surface of said second substrate, wherein said projecting memberis formed of or coated with a layer of a second electrically conductivematerial; and compressing the projecting member of said second substrateinto the aperture of said first substrate, to locally plastically deformand shear the first and second electrically conductive materials, in anamount effective to form a hermetic cold weld and electrical connectionbetween the first and second electrically conductive materials.
 11. Themethod of claim 1, wherein the first and second electrically conductivematerials are gold.
 12. The method of claim 10, wherein the first andsecond electrically conductive materials are gold.